Decyanation

ABSTRACT

Processes are disclosed for providing in situ generated cyanic acid and simultaneously preparing certain carboxamides which have a tertiary aliphatic substituted ammonium or pyridinium group substituted on the alpha carbon atom.

This is a continuation-in-part of Ser. No. 725,571 filed Sept. 22, 1976,now U.S. Pat. No. 4,110,424, which is a continuation-in-part of Ser. No.627,373, filed Oct. 30, 1975 now abandoned, in the names of Howard C.Haas and Robert D. Moreau.

This invention relates to novel polymeric quaternary salts which can beused to produce cyanic acid and polymeric carboxamides. The currentavailable way to provide cyanic acid is by cracking cyanuric acid andstabilizing the resulting cyanic acid. Cyanic acid is volatile andpolymerizes explosively unless properly stabilized. Providing it for insitu reaction removes the problem of handling it.

Most organic acids undergo decarboxylation if they are heated to asufficiently high temperature. The presence of strongly electronwithdrawing substituents on the α-carbon atom greatly facilitates theease with which carbon dioxide is released. The decarboxylation reactionis normally heterolytic, the R group departing with an electron pair.

    RCOO.sup.- →R.sup.- +CO.sub.2

Enol forms of the acid are not generally involved in decarboxylation.With β-carbonyl containing acids, cyclic hydrogen bonded structures,however, are believed to play a role in the decarboxylation mechanism.The decarboxylation of malonic acid, for example, is usually written as:##STR1##

The pyrolysis of amides is generally a very complex reaction. Uponheating they can dehydrate to form nitriles and, in some cases, ammoniais split out to yield imides, particularly if stable cyclic imides arepossible.

It is the primary object of the present invention to provide a novelmethod of decyanating quaternary salts of certain amides containinghighly positively polarized α-carbon atoms to form α-pyridiniumcarboxamides. It is, further, an object of this invention to provide asource for generating, in situ, cyanic acid.

Other objects of the invention will in part be obvious and will in partappear hereinafter.

The invention accordingly comprises the method involving the severalsteps and the relation and order of one or more of such steps withrespect to each of the others which are exemplified in the followingdetailed disclosure, and the scope of the application of which will beindicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed description taken inconnection with the accompanying drawing wherein:

FIG. 1 is a graphic representation of the infrared spectrum of polyvinylalcohol (the dashed curve) and of the partial carbamate ester ofpolyvinyl alcohol (the solid curve).

It has now been discovered that certain organic amides which containhighly positvely polarized α-carbon atoms preferentially lose cyanicacid on heating. This reaction involves the thermal loss of cyanic acid(HOCN⃡HNCO) by an amide in much the same manner that an organic acidloses carbon dioxide during decarboxylation. The reaction will bereferred to as a decyanation. This decyanation proceeds in a mannerwhich is completely analogous to the decarboxylation of malonic acid.The reaction provides a useful way of providing cyanic acid in situ foruse in reactions utilizing cyanic acid.

Compounds of the following structure may be decyanated according to thisinvention ##STR2## where R is selected from one group consisting ofhydrogen and alkyl groups containing from one to twenty carbon atomsinclusive, Q is selected from the group consisting of tertiary aliphaticsubstituted ammonium groups, polymeric tertiary aliphatic substitutedammonium groups, pyridinium, substituted pyridinium, polymericsubstituted pyridinium, quinolinium and iso quinolinium where R ishydrogen and from the group consisting of pyridinium, substitutedpyridinium, polymeric substituted pyridinium and iso quinolinium groupswhen R is alkyl, and X is selected from the group consisting of bromide,chloride and iodide.

The following polymeric compounds are included in this formula ##STR3##wherein R' is selected from the group consisting of hydrogen and n-alkylgroups containing from one to twenty carbon atoms inclusive, R² and R³are lower alkyl groups having from one to four carbon atoms and X is asdefined above.

As noted, n-alkyl groups may contain from one to twenty carbon atomsinclusive, as for example, methyl, ethyl, n-propyl, n-butyl, n-decyl,n-dodecyl and the like. When R is n-decyl, and Q is pyridinium, forexample, the α-pyridinium carboxamide formed by way of this invention isuseful as a wetting agent.

Examples of these compounds are the pyridine or isoquinoline quaternarysalts of 2-bromomalonamide, 2-methyl-2-bromomalonamide or2-n-decyl-2-bromomalonamide; the polymeric quaternary salts prepared byquaternizing poly 4-vinyl pyridine with bromomalonamide; the trimethylammonium salt of bromomalonamide; the p-phenyl pyridine quaternary saltof bromomalonamide; the p-phenyl pyridine quaternary salt ofbromomalonamide; the quinoline quaternary salt of 2-bromomalonamide andthe polymeric quaternary salts prepared by quaternizing polyvinyldimethyl amine with bromomalonamide.

The polymeric quaternary salt of this invention may be heated in solidform or in solution to provide cyanic acid and the polymericcarboxamide. If the reaction is run in solution the choice of solvent islimited by few parameters. In addition to being a solvent for thestarting material, the solvent must not, of course, react with thestarting material; nor should it react with the product. The boilingpoint of the solvent, at the pressure used, should be high enough sothat the reaction can occur above about 100° C. and preferably at about150°-170° C. without the solvent boiling. The reaction may, of course,be run in a closed system such as a steel bomb in a solvent with a lowerboiling point. m-Cresol can be used as a solvent in this reaction.

A preferred embodiment of this invention involves the cracking of thepyridine quaternary salt of 2-methyl-2-bromomalonamide in m-cresol at160°-170° C. which cracking yields only two isolatable products,cyanuric acid formed by the polymerization of cyanic acid and N-2propionamido pyridinium bromide. ##STR4##

The above equation has been written with a cyclic hydrogen bondedstructure for the quaternary salt (I) which uses the tautomeric form ofone amide group. A mechanism similar to this equation can be written inwhich the cyclic hydrogen bonded structure involves the -OH of thetautomerized group rather than the imine residue, in which casetautomeric isocyanic acid (HNCO) would be split out. It is not knownwhich mechanism prevails. Nor does this make a difference since cyanicand isocyanic acid normally are in tautomeric equilibrium with theiso-structure predominating. It is to be understood that neither theproduct nor the process of this invention is limited by this proposedmechanism.

There is reliable evidence that (I) does exist in some cyclic hydrogenbonded imino form, at least in the solid-state. The infrared spectra ofprimary amides normally contain two absorption bands in the 1600-1700cm⁻¹ region which are assigned to carbonyl stretching and --NH₂deformation. Spectra taken (KBr discs) of malonamide,2-methyl-malonamide and 2-bromo-2-methyl malonamide, all contain thesetwo absorptions. The infrared spectrum of (I) (KBr) disc) shows at least7 bands in the 1600-1720 cm⁻¹ range. Comparison of this spectrum withthat of deuterated I (dry KBr and Nujol mull;) shows that the band at1627 cm⁻¹ has shifted slightly to 1630 cm⁻¹ and must be assigned tovibrations of the N-alkylated pyridinium ring which normally occur atthis frequency. The 1600 cm⁻¹ band has been shifted to a much lowerfrequency and its origin is an N--H or NH₂ bending deformation. In thespectrum of deuterated I, at least five bands still remain between 1640and 1700 cm⁻¹ and these undoubtedly arise from hydrogen bonded andnonhydrogen bonded carbonyl and imino forms of I. The infrared spectrumof (II) (KBr disc) is that of a normal primary amide since thepossibility for cyclic hydrogen bonded structures is no longer present.Pyridinium ring absorption is again about 1630 cm⁻¹. The --C═Ostretching vibration is at 1688 cm⁻¹ with the --NH₂ deformationappearing as a shoulder on the lower frequency side of the carbonylabsorption. If the infrared spectrum of (I) is taken indiimethylsulfoxide, an excellent solvating and hydrogen bond breakingsolvent, the carbonyl and --NH₂ absorptions revert to those of a normalprimary amide.

It has been shown that cyanic acid can be produced from solutions ofthese quaternary salts. For example, in our parent application Ser. No.725,571, in a preferred embodiment there was provided a solution inm-cresol of an amine-substituted dye which dye must be stable at150°-170° C. For example, a solution of 1-amino-4-hydroxy-anthraquinonemay be provided and divided into two portions. To one portion is addedthe pyridine quaternary salt of 2-bromo-2-methylmalonamide. Each portionis then heated to approximately 160° for about an hour and then cooled.It is found that the portion containing the pyridine quaternary salt haschanged color. It is more red in appearance than is the control portion.This change is consistent with the formation in the solution of thesubstituted urea ##STR5##

The decyanation reaction of this invention may be utilized to provideimages by the imagewise thermal decyanation of a polymeric quaternarysalt. In this embodiment, the polymer is intimately associated with adye containing an amine group. This mixture of polymer and dye isprovided in a layer which can be heated to approximately 150°-200° in animagewise manner, for example, by contacting the layer with a metal formbearing a relief character, an image. Upon this thermal contact thepolymer decyanates releasing cyanic acid which reacts with the aminegroup of the associated dye changing the color of the dye.

The present invention will be illustrated in greater detail inconjunction with the following specific examples which are intended tobe illustrative only and should not be taken in a limiting sense.

EXAMPLE I

Diethyl methyl malonate was reacted with aqueous concentrated ammonia toyield 2-methyl-malonamide which, after recrystallization from methanol,had a melting point of 213°-14° (uncorr.). The infrared spectrum is thesame as given by C. J. Pouchert, Spectrum 339F in the Aldrich Library ofInfrared Spectra, Aldrich Chemical Co., 1970, and the nuclear magneticresonance spectrum in dimethylsulfoxide integrated properly for thevarious protons. Bromination of 2-methyl malonamide was carried out withbromine in glacial acetic acid following Stevens and Ward as reported inJ. Chem. Soc. vol. 125, page 1324 (1924). Two recrystallizations frommethanol gave a melting point of 177° C. (uncorr.), reported 172° C.

The pyridine quaternary salt of 2-bromo-2-methylmalonamide was readilyprepared by dissolving the bromo compound in excess pyridine and heatingthe solution for several hours at 60° C.

The quaternary salt was filtered off and recrystallized twice frommethanol, m.p.=227° C. (uncorr., with decomposition). The salt is watersoluble and reacts instantly with silver nitrate solution. Analysisgave: C, 39.5; H, 4.59; N, 15.0; Br, 28.8. Theory: C, 39.4; H, 4.38; N,15.3; Br, 29.2. D₂ O rapidly exchanges the amide protons, and NMR is incomplete agreement with the assigned structure.

Decyanation was carried out as follows. The pyridine quaternary salt(0.5 g.) was dissolved in 5 ml. of warm m-cresol and the solution heatedat 160°-70° C. for 50 min. in an oil bath. Evolved vapors are neutral toindicator paper. On cooling the solution in a refrigerator, a whitesolid separated from solution. This solid was filtered off, washed witha small amount of 1/1 methanol-ether and air dried. It did not melt upto 350° C. and was readily identified as pure cyanuric acid bycomparison of its infrared spectrum (KBr disc) with that of an authenticsample. The m-cresol filtrate was poured with stirring into a largeexcess of diethyl ether. A tacky material separated, which was againreprecipitated from a very small amount of methanol into excess ether.The tacky precipitate was recrystallized from methanol/ether to yield awhite crystalline solid having a m.p. of 189°-90° C. (uncorr.). It wasreadily water soluble and gave a strong test for soluble bromide. TheNMR spectrum (in DMSO) is in complete agreement with the assignedstructure for N-2-propionamideo pyridinium bromide. Analysis gave: C,41.8; H, 4.89; N, 12.1; Br, 34.5. Theory: C, 41.6; H, 4.80; N, 12.1; Br,34.6. In three repeats of this decyanation reaction, no other productswere obtained. Depending on the exact conditions (relativeconcentrations of quaternary salt (1) and m-cresol, temperature andtime), cyanuric acid may or may not be isolated. Therefore, cyanic acidmay escape by volatization, or polymerize in situ; or it may react withadded materials to give desired by-products. The yield of crudeN-2-proionamido pyridinium bromide is almost quantitative.

EXAMPLE II

2-Bromomalonamide, m.p.=181° c., was prepared following Backes, West,and Whiteley, J. Chem. Soc., Trans. 1, volume 119, p. 359 (1921). Thepyridine quaternary salt, m.p.=224°-5° C. (uncorr.) was prepared byheating bromomalonamide in methanol solution with excess pyridine.Analysis gave: C, 37.2; H, 3.92; N, 16.0; Br, 30.9. Theory: C, 36.9; H,3.84; N, 16.1; Br. 30.8. Decyanation and isolation was carried out asdescribed in Example I for the salt of 2-bromo-2-methyl-malonamide. Thedecyanation product, N-2-acetamido-pyridinium bromide, m.p.=200° C.,(uncorr.), had the following analysis. Found: C, 39.3; H, 4.28; N, 13.1;Br, 37.0. Theory: C, 38.8; H, 4.15; N, 12.9; Br, 36.9.

EXAMPLE III

A polymeric quaternary salt, designated as Polyquat A, was prepared byquaternizing poly 4-vinylpyridine with bromomalonamide. Bromomalonamide(6 g, 0.033 m) dissolved in 100 ml. of hot methanol was added to asolution of poly 4-vinyl pyridine (10.5 g, 0.1 m) in 200 ml. of hotethanol. The solution, heated on a steam cone, gelled afer ten minutes.

Heating was continued for an additional 30 minutes. The polymer wascoagulated by adding excess acetone, washed successively with ethanol,acetone and ether and vacuum dried. The polymer is a yellow powder whichdissolves in water to yield a yellow solution having a pH of about 7.5.The color suggests that the polymer exists partially as the polymericylid zwitterion. ##STR6## Addition of dilute acid to the aqueoussolution bleaches the color whereas the addition of dilute alkaliproduces a deep yellow color. Polyquat A was 33% quaternized, based onelemental analysis for bromide.

A second polymeric quaternary salt, designated as Polyquat B wasprepared similarly except that 100% quaternization was sought.Bromomalonamide (10 g., 0.055 m) in 150 ml. of hot methanol was added toa solution of poly 4-vinylpyridine (5 g., 0.047 m) dissolved in 150 ml.of ethanol. The solution was heated for 2 hours on a steam cone and thesolvents allowed to almost completely distill off. Additional methanolwas added and the swollen polymer filtered off, washed with hotmethanol, ether and vacuum dried. The polymer is a very light yellowpowder which dissolves in distilled water to give an almost colorlesssolution of about pH=5.6. The lighter color suggests that because of thehigher degree of quaternization and lower free base content, less ylidstructure is present. Elemental analysis of Polyquat B indicated 99.5%quaternization. Potentiometric analysis of bromine indicated a somewhatlower degree of quaternization.

Final purification of both Polyquats A and B was accomplished bydialysis of their stirred water solutions for several hours againstdistilled water using regenerated cellulose dialysis tubing. Thepolymers were isolated by freeze drying and final drying wasaccomplished at 45° C. under vacuum over phosphorus pentoxide.

Films of Polyquat B containing the disodium salt of 3,3'-[4,4'biphenylylene bis (azo)] bis[4-amino-1-naphthalenesulfonic acid] (knownas Congo Red) were cast from water and air dried. These films wereheated to about 170°-180° C. in film form on glass or pulverized in acapillary. In both cases there was an evident decrease in the colorintensity and a hypsochromic shift in color. Congo Red heated in acapillary at the same time and rate did not show either change at thistemperature.

EXAMPLE IV

One gram of 2-bromomalonamide (m.p. 181° C.) was heated with an excessof pure trimethylamine in a steel bomb at 100° C. for 18 hours. Thesolid in the bottom of the bomb after evaporation of the excess aminewas recrystallized from ethanol containing a small amount of methanol;m.p=195°-6° C. with no foamsing. Above 200° C. the brom melt rises inthe capillary. This product is water soluble and contains bromide ion.Analysis showed 33.1% Br (theoretical value 33.3% Br) for ##STR7## Theinfrared spectrum of the above compound shows a carbonyl stretch at 1720cm⁻¹. Elemental analysis gave carbon 30.26%; hydrogen 5.99% and nitrogen17.76%. Theoretical values are: carbon 30.0%, hydrogen 5.87% andnitrogen 17.5%. The NMR in deuterated dimethyl sulfoxide integratesproperly.

One half gram of the quaternary salt of the above compound was dissolvedin excess m-cresol (about 5 ml.), and heated for one hour at 160° C. inan oil bath. The product was precipitated into ether and recrystallizedfrom alcohol/ether. The melting point was 181° C. but was not sharp. Amixed melting point with the above compound showed a large depression toabout 160° C. showing that the product was not the above compound. Theproduct is water soluble and contains bromide ions. Analysis for bromidegave 40.53% as opposed to a theoretical bromide value of 40.51% for thedecyanated product ##STR8##

EXAMPLE V

Polyvinyl alcohol of a low degree of polymerization dissolved inm-cresol solution was treated with the pyridine quaternary salt of2-methyl-2-bromomalonamide and the reaction mixture heated at 160°-170°C. for one hour. Polymer was recovered in a fibrous form byprecipitation into methanol, was purified by two reprecipitations fromwater into a large excess of methanol and was dried under vacuum at 45°C. over phosphorous pentoxide. Analysis gave 1.15 percent nitrogen andthe infrared spectrum indicates that the product is a copolymer of vinylalcohol and vinyl carbamate. FIG. 1 is a graph of the infrared spectrumof (a) the starting material, polyvinyl alcohol (the dashed curve); and(b) the product formed after th decyanation and reaction of theliberated cyanic acid with the polyvinyl alcohol (the solid curve)showing it to be in the partial carbamate ester of polyvinyl alcohol.

EXAMPLE VI

One-half gram of the pyridine quaternary salt of2-bromo-2-methylmalonamide as prepared in Example I was dissolved in 5ml. of warm m-cresol and the solution heated at 112°-117° C. for 17hours in an oil bath. After this heating the solution was poured withstirring into 100 ml. of ether. An almost white precipitate was filteredout and dissolved in a minimum amount of methanol. On a steam cone,ether was added to the methanol solution dropwise until a slight hazedeveloped. The solution was allowed to cool, first to room temperatureand then in a refrigerator. The crystals formed, representing about 20%of the starting material, were filtered off and dried. They melted inthe temperature range 172°-185° C. Infrared analysis indicated that theywere starting material contaminated with a little of the decyanationproduct. Washing these crystals with a small amount of methanol resultedin raising their m.p. range to 205°-215° C. The m.p. of pure startingmaterial is 227° C.

The methanol filtrate was poured into an excess of ether. Theprecipitate formed, representing about 80% of the starting material, wascollected and vacuum dried. It melted at 173°-182° C. The infraredspectrum was that of the decyanated product. Pure decyanated productmelts at 180°-190° C.

It can be seen that by allowing longer reaction times the decyanationcan be carried out at lower temperatures. This method of generatingcyanic acid is thereby useful in situations wherein it is desired toreact in situ generated cyanic acid with compounds which are not stableat much higher temperatures, or in situations wherein a slow release ofin situ generated cyanic acid is desired.

EXAMPLE VII

The isoquinoline quaternary salt of 2-bromomalonamide was prepared byheating bromomalonamide in methanol solution with excess isoquinoline. Agood yield of the quaternary salt was filtered off and recrystallizedfrom methanol, m.p.=234° (uncorr.). It was water soluble and reactedinstantly with silver nitrate solution. Carbonyl absorption was between1700 and 1720⁻¹. Differential thermal analysis showed a transition at130°-135° C., and a melting starting at 225° C. followed by thedecyanation exotherm. Thermogravimetric analysis showed the start of arapid gross decomposition at approximately 240° C.

EXAMPLE VIII

The isoquinoline quaternary salt of 2-bromo-2-methyl malonamide wasprepared similiarly. It was water soluble, had a melting point of186°-190° C., and reacted instantly with silver nitrate solution. Theinfrared spectrum showed a carbonyl absorption at 1700⁻¹. Differentialthermal analysis showed melting beginning at 183° C. followed by thedecyanation exotherm. Thermogravimetric analysis showed a rapid grossdecomposition beginning at 198° C.

EXAMPLE IX

The quinoline quaternary salt of 2-bromomalonamide was prepared byheating a gram of 2-bromomalonamide with excess quinoline for 4 hours at65° C., precipitating into ether, dissolving the precipitate in aminimum quantity of warm methanol, and adding ether to the point of hazeformation. After decanting the solvent, methanol was added to theresulting oil to give crystals which melted at 210°-212° C. and showed acarbonyl absorption in their infrared spectrum at 1710⁻¹. The productwas water soluble and gave a good test for bromide ion, reactinginstantly with silver nitrate solution. Differential thermal analysisshowed a melting point at 207° C. followed by the decyanation exotherm.Thermogravimetric analysis showed rapid gross decomposition atapproximately 225° C.

Since certain changes may be made in the above process without departingfrom the scope of the invention herein involved, it is intended that allmatter contained in the above description or shown in the accompanyingdrawings shall be interpreted as illustrative and not in a limitingsense.

What is claimed is:
 1. A polymeric compound of the structure ##STR9##where Q is a polyvinyl pyridinium, R is hydrogen or a n-alkyl groupcontaining from one to twenty carbon atoms inclusive and X is bromide,chloride or iodide.
 2. A compound as defined in claim 1 wherein Q ispoly-4-vinyl pyridinium.
 3. A compound as defined in claim 2 wherein Ris hydrogen and X is bromide.